1. Technical Field
This invention relates to an ink jet record head for ejecting ink droplets through nozzle openings with pressure fluctuations in pressure generation chambers, thereby recording images and characters on record paper.
2. Related art
Generally, an ink jet record head shown using piezoelectric vibrators as pressure generation elements is designed as in FIGS. 9 and 10, which will be hereinafter referred to simply as a record head. The record head comprises a head case 10 and a flow passage unit 9 fixedly secured to the unit fixation face of the head case 10 (the top face thereof in FIG. 9) with an adhesive, etc. The flow passage unit 9 is made up of a nozzle plate 6, a flow passage board 4, and a vibration plate 8 stacked one on another.
The nozzle plate 6 is formed with a large number of nozzle openings 5 arrayed in rows (in a direction perpendicular to the plane of FIG. 9). The flow passage board 4 is formed with flow passages, which include pressure generation chambers 1 communicating with the respective nozzle openings 5, ink reservoirs 2 for temporarily storing ink to be ejected through the nozzle openings 5, and ink supply passages 3 for supplying ink from the ink reservoirs 2 to the pressure generation chambers 1.
The pressure generation chambers 1 are arrayed to correspond in location to the respective nozzle openings 5, and each ink reservoir 2 is elongated along the row of the associated pressure generation chambers 1.
The vibration plate 8 is a composite plate of a resin sheet and a stainless sheet, and is formed with ink supply ports 12 (not shown in FIG. 9) for introducing ink into the ink reservoirs 2.
The head case 10 is formed with windows 16 in the portions corresponding to the respective rows of the pressure generation chambers 1 for exposing piezoelectric vibrators 7 therefrom. In FIG. 9, numeral 18 denotes a fix board for fixing the piezoelectric vibrators 7, and numeral 19 denotes a chamber for housing a piezoelectric vibrator unit comprising the piezoelectric vibrators 7 fixed onto the fix board 18.
However, in the record head, when an ink cartridge is attached or detached, an air bubble 11 may enter and flow into the ink reservoir 2. If the air bubble 11 thus enters the ink reservoir 2, as shown in FIGS. 10 and 11, the air bobble 11 is caught in an end part of the ink reservoir 2 and grows, and flows into the pressure generation chamber 1 because of the reciprocating operation of a carriage, vibration, etc., easily causing a print failure of so-called dot dropout, etc.
The bubble 11 entering the ink reservoir 2 is forcibly sucked and removed through the nozzle opening 5 by the suction operation, etc., as cleaning. However, the flow velocity of ink during the sucking operation is low in the proximity of the end part of the ink reservoir 2, and the air bubble 11 is likely to remain without being discharged, easily causing a print failure of so-called dot dropout, etc.
It is therefore an object of the invention to provide an ink jet record head for making it possible to reliably remove air bubbles in ink reservoirs by the suction operation of cleaning, etc.
To achieve the above-mentioned object, the present invention provides an ink jet record head including:
pressure generation chambers arrayed in at least one row and associated with at least one nozzle openings;
at least one common ink reservoir elongated along a row direction of the pressure generation chambers;
ink supply passages communicating the at least one ink reservoir with the pressure generation chambers; and
pressure generation elements for causing the pressure generation chambers to generate pressure,
wherein ink reservoir side opening parts of the ink supply passages in the proximity of an end part of the ink reservoir are arranged closely as compared with ink reservoir side opening parts of the ink supply passages in the proximity of a central part of the ink reservoir.
That is, in the ink jet record head of the invention, the ink reservoir side opening parts of the ink supply passages in the proximity of the end part of the ink reservoir are arranged closely as compared with the ink reservoir side opening parts of the ink supply passages in the proximity of the center part of the ink reservoir. Thus, if an air bubble enters the ink reservoir and remains in the proximity of the end part of the ink reservoir, the suction forces from the closely arranged ink supply passages are combined and the air bubble is strongly sucked, etc., during cleaning, etc., and is easily discharged from the ink reservoir. Although the suction force for each ink supply passage is weak, the combined suction force acting on the air bubble becomes strong and thus the air bubble can be discharged securely with a small suction force, etc. Thus, it is possible to reduce costs because of miniaturization of a suction pump, etc., increase the work speed because of shortening the suction time, and decrease the sucked ink amount, and occurrence of print failures in the presence of the air bubble remaining in the ink reservoir is also decreased.
In the ink jet record head of the invention, if the inertance acting on each pressure generation chamber in association with a flow passage from the opening part of the ink supply passage to the nozzle opening is set substantially equal, the inertance acting in each nozzle opening is equal and thus the ejection characteristics of the ink droplet speed, the ink droplet volume, etc., of each nozzle opening can be made substantially uniform and the print quality is stabilized.
The expression xe2x80x9csubstantially equalxe2x80x9d means that the inertance is made uniform.
In the ink jet record head of the invention, if the inertance is made substantially equal by adjusting the cross-sectional areas of the ink supply passages, the inertance of one pressure chamber and that of another pressure chamber can be made uniform comparatively easily.
In the ink jet record head of the invention, if a narrow area having a cross-sectional area less than that of another portion (for example, the central part of the ink reservoir) is formed in the proximity of the end part of the ink reservoir, a plurality of ink supply passages positioned on the end part side of the ink reservoir from the proximity of the entrance of the narrow area effectively function to discharge an air bubble of such a size as to be caught in the entrance to the narrow area. Accordingly, an air bubble of the size comparatively hard to be discharged can be easily discharged. Alternatively, a large air bubble is caught in and stops at the entrance of the narrow area, only a small air bubble comparatively easily discharged enters the narrow area, and the large air bubble comparatively hard to be discharged does not enter the proximity of the end part of the ink reservoir. Thus, a print failure in the proximity of the end part can be prevented more effectively In the ink jet record head of the invention, if the ink flow passages are formed with island parts, it is possible to reduce print failures due to the presence of the air bubble remaining in the ink reservoir.
In the ink jet record head of the invention, if the inertance is made substantially equal by adjusting at least one of the width and length of the island parts, the inertance of one pressure chamber and that of another pressure chamber can be made uniform comparatively easily. In this case, either or both of the width and length of the shallow part may be adjusted.
If the ink jet record head of the invention comprises a nozzle plate formed with the nozzle openings, a flow passage formation plate formed with flow passages corresponding to the pressure generation chambers, the ink reservoirs, and the ink supply passages, and a seal plate for closing openings of the flow passages, it is possible to deduce print failures due to the presence of the air bubble remaining in the ink reservoir.
In the ink jet record head of the invention, if the flow passage formation plate is formed by a plurality of laminated metal plates formed with openings used as the flow passages, the flow passage formation plate in which the ink supply passages are bent, etc., in the proximity of the end part of the ink reservoir to closely arrange the opening parts of the ink supply passages can be manufactured easily. Also, the formation plate in which the widths of the ink supply passages are changed to make the inertance of each ink supply passage, etc., substantially equal can be manufactured easily.
In the ink jet record head of the invention, if the flow passage formation plate is formed by a plurality of laminated photosensitive resin sheets formed with openings used as the flow passages by light exposure, the plate in which the ink supply passages are bent, etc., in the proximity of the end parts of the ink reservoirs to closely arrange the opening parts of the ink supply passages can be manufactured easily. Also, the plate in which the widths of the ink supply passages are changed to make the inertance of each ink supply passage, etc., substantially equal can be manufactured easily.
In the ink jet record head of the invention, if the flow passage formation plate is made of monocrystalline silicon formed with the flow passages by etching, the plate formed with the ink supply passages having the island parts can be manufactured comparatively easily. Further, in the case of the ink supply passages having the island parts, the inertance of one pressure chamber and that of another pressure chamber can be made substantially equal by simply adjusting the width and/or length of the island part.
In the ink jet record head of the invention, if the pressure generation chambers communicating with one of an opposed pair of ink reservoirs and the pressure generation chambers communicating with the other thereof are arranged alternately, if the nozzle openings are disposed like a staggered arrangement to communicate with a respective one of the pair of ink reservoirs facing each other, or if each of the nozzle openings is disposed on the side of the associated pressure generation chamber away from the associated ink reservoir, the spacing between the adjacent opening parts of the ink supply passages is likely to be wide and an air bubble becomes hard to be discharged accordingly and in addition, the ink flow velocity in the proximity of the end part of the ink reservoir during the suction is like to be lowered. Therefore, the invention is effectively applied to these arrangement to provided the remarkable effect of positively discharging an air bubble in the proximity of the end part.
The present disclosure relates to the subject matter contained in Japanese patent application No.2000-010655 (filed on Jan. 19, 2000) and Japanese patent application No.2000-395378 (filed on Dec. 26, 2000), which are expressly incorporated herein by reference in their entireties.